1. Field
Apparatuses consistent with exemplary embodiments relate to a lens for changing light distribution of incident light, and a bulb-type light emitting device lamp having a large light distribution range by employing the lens.
2. Description of the Related Art
A light emitting diode (LED) is a semiconductor light emitting device that converts an electrical signal into light by using a characteristic of a compound semiconductor. A semiconductor light emitting device such as an LED has a long lifetime, uses a low voltage, and demands small power consumption, compared to another type of light emitting device. Also, a semiconductor light emitting device may have a fast response speed and excellent shock-resistance and may be small and light-weight. When required, a semiconductor light emitting device may generate and emit light having different wavelengths according to types and composition of a semiconductor used. Recently, lighting devices using a high-luminance light emitting device chip have been replacing existing fluorescent lamps and incandescent electric lamps.
For example, in general, an LED bulb may be formed of a cap, a heat radiation structure, a driving circuit, a printed circuit board (PCB), an LED, and a cover. In general, the cover is formed of a hemisphere-shaped glass material or a semicircle-shaped plastic material such as acryl, polycarbonate, or the like. Also, in order to form a screen on the LED in the LED bulb, with respect to a glass cover, a white diffusion coating is formed on an inner surface of the glass cover, and with respect to a plastic cover, a diffusion material is mixed in a cover material so as to realize a light diffusion effect.
However, an illumination lamp using a semiconductor light emitting device emits light in only a forward direction, not in every direction, and thus a light diffusion characteristic of a illumination lamp using a semiconductor light emitting device is highly different from that of an existing incandescent electric bulb. For example, an LED bulb emits the greatest amount of light in a forward direction, 0° direction), and the amount of light emission decreases as an angle increases, and thus the amount of light emission is almost 0 at about ±90°. On the other hand, the amount of light emission of a general incandescent electric bulb does not decrease and is almost uniform from 0° direction to about ±130° direction. Accordingly, an LED bulb and a general incandescent electric bulb are highly different regarding full width at half maximum (FWHM) such that a FWHM of an LED bulb is about 130° whereas a FWHM of a general incandescent electric bulb is about 260°. The difference occurs because a filament used in a general incandescent electric bulb emits light in every direction (range of 360°) whereas an LED emits light in only a forward direction (range of about 120°). Due to the difference, when an LED bulb is used in a general illumination lamp, light diffusion and luminous intensity is significantly different from those that users are familiar with. This may be an obstacle to spreading of an LED bulb.